Physiology of muscle contraction


Published on

The muscle are biological motors which convert chemical energy into force and mechanical work.
This biological machinery is composed of proteins – which is actomyosin and the fuel is ATP.
With the use of muscles we are able to act on our environment.

Published in: Education
No Downloads
Total views
On SlideShare
From Embeds
Number of Embeds
Embeds 0
No embeds

No notes for slide

Physiology of muscle contraction

  1. 1.  Importance of muscular movement Muscles are biological machines. Functional characteristics of muscles. Muscle organization-skeletal , plain and cardiac muscles – comparison Skeletal muscle-structure, fibrillar system, contractile proteins Energy sources of muscle –ATP, CP and glucose. Cori’s lactic acid cycle. Events of muscle stimulation. Molecular events of muscle contraction and relaxation. Theories of muscle contraction Summary
  2. 2.  Movement is the basic property of living systems. Animals move by contracting muscles. Muscle contraction is one of the key processes of animal life. Movement of muscle is the prerequisite for vital activities like digestion, reproduction, excretion and circulation.
  3. 3.  Gives shape and structure to the body. Enables animals to maintain erectSkeletal muscle  posture.  Brings about movement  Helps the animal to secure food and shelter and escape from danger.  Helps to communicate its wishes.  Assist breathing movements  Aids hearing and vision.Smooth muscle  Helps digestion, excretion, reproduction and circulation.  Propels digested food, body fluids, glandular secretions and waste products.  Pumps blood to all parts of the body.
  4. 4. The function of Muscles are muscle is to convert The chemical energybiological machines chemical energy into is obtained frommade up of proteins. mechanical work ATP and CP and force.
  5. 5. Excitability • the ability to receive and respond to stimuli.Conductivity • The ability to receive a stimulus and transmit a wave of excitation (electrochemical activity)Contractility • the ability to shorten forcibly when stimulated.Extensibility • the ability to be stretched or extended. Elasticity • The ability to bounce back to original length
  6. 6. Plain muscle QuickSlow Smooth Actingmuscle Un-striped/ Muscle muscle Non- striated muscle Fast Striped / Skeletal moving Striated Visceral In- muscle voluntary muscle muscle muscle muscle Voluntary muscle
  7. 7.  Elongated spindle shaped muscle fibers with thickened central belly and two pointed terminals. The cytoplasm is granular without any cross striations. A rod like nucleus is placed in the center. Myofibrils are arranged in longitudinal axis. Found alimentary canal, respiratory tract, uterus, urinary bladder, arteries and veins.
  8. 8.  Branched and form a net work. The two adjacent muscle cells form tight junctions in the form of intercalated discs. Exhibit faint transverse striations. Innervated by autonomic nerve fibers. Nucleus is round or oval in shape. Fewer myofibrils with greater amount of sarcoplasm for more storage of glycogen. Sarcolemma is indistinct.
  9. 9.  Complex, elongated, cylindr ical and fast moving muscles. Each fiber is multinucleated with transverse and longitudinal striations. The cytoplasm is composed of myofibrils with many myofilaments. Large number tubules run through sarcoplasm and form sarcoplasmic reticulum. The sarcosomes or mitochondria supply ATP to the myofibrils..
  10. 10. parameters striped muscle Plain muscle Heart muscleOccurrence Associated with Present in the visceral Present in the heart Skeletal system organsShape long Cylindrical Spindle shaped Short cylindricalStriations Longitudinal and Only longitudinal Faint Longitudinal and transverse stripes stripes transverse stripesNucleus multinucleated Single centrally placed Single centrally placedSarcolemma Well defined and tough Not well defined Not well definedBranching No branching No branching branchedNerve supply somatic autonomic autonomicRhythmicity Not present present presentContractility Fast Slow Medium fastTetanus possible Partially possible Not possible
  11. 11.  Muscle displays dark or A bands or anisotropic bands and light or I bands or isotropic bands. Each A band has a less denser region called H band or Hensen’s line. In each I band, there is a dense cross line called Z band. The area between two adjacent Z lines is called a sarcomere.
  12. 12.  The myofilaments consists of thick myosin filaments and thin actin filaments and are arranged in an overlapping manner. The myosin filaments bear thick knob like projections called cross bridges. The sarcoplasmic reticulum is made up of longitudinal system of canals between myofilaments. There is also T system of canals.
  13. 13. Water• Muscle contains about 75-80% of water.• Water provides a good medium for inorganic and organic compounds.• Water reduces friction and dehydration of muscles.Proteins• Muscle consists 3 types of proteins:- structural proteins, contractile proteins and enzymatic proteinsMinerals• Calcium ions of sarcoplasm initiates muscle contraction.• Magesium ions are important for muscle contraction.• sodium and Potassium ions set the action potential.Organic compounds• Muscle is a storehouse of glycogen and oxidation of glycogen provides energy.• The activity of muscle is proportional to the amount of phospholipids.• ATP is the primary source of energy for muscle contraction.
  14. 14. Structural •Collagen provides toughness •Elastin offers elasticity to proteins muscles •Myosin, actin, tropomyosin, andContractile troponin. •Myosin constitutes 35% and actin proteins 15% of total proteins. Enzymatic •Adenosine triphosphatase •Creatine phosphatase proteins •Lactic dehydrogenase
  15. 15. Myosin – prime contractile element of muscle.Have triple helical structure.Molecular weight is 420,000.Hydrolysis of myosin with enzyme trypsin yieldstwo fractions – heavy meromyosin (HMM) andlight meromyosin (LMM).Hmm acts as an enzyme ATPase for splitting ofATP into ADP and Pi.Hydrolysis of HMM with papain yields sub-fragment 1 and sub-fragment 2.
  16. 16.  Non-contractile and elastic in nature. Made up of spherical molecules (G- actin). Molecular weight =60,000. G-actin polymerizes into double stranded helices called fibrous or F- actin. G-actin +ATP -F-actin +ADP +Pi.
  17. 17.  1 mole of actin +3 mole of myosin - actomyosin (super- precipitation). Actomyosin +ATP—ca++, mg++actin +myosin +ADP
  18. 18.  Non-contractile, fibrous protein. It plays important role in in sensitizing actin and myosin molecules to calcium ions. This sensitivity is important in order to switch contraction on or off. Tropomyosin invertebrates A Tropomyosin Tropomyosin vertebrates B
  19. 19.  Troponin occurs at intervals on the actin filament. Troponin takes up ca++ ions from the sarcoplasm to initiate muscle contraction. In muscle troponin and tropomyosin combines to form troponin- tropomyosin system.
  20. 20. Molecular MolecularEnergy Events of events of events of muscleSources muscle muscle stimulation contraction relaxation
  21. 21. • ImmediateCreatinePhosphate • Phosphagen system • Short term Anaerobic glycolysis • Lactic acid system • Long term Aerobic • Glucose, fattyglycolysis acids, Amino acids
  22. 22. Creatine phosphate CP Adenosinetriphosphate Glucose ATP Chemical Energy sources
  23. 23.  ATP is the immediate source of energy for muscle contraction. The break down of phosphate bond of ATP releases maximum energy.Anaerobic glycolysis:Glucose - 2 moles of lactic acid +8ATPs.Aerobic glycolysis coupled with Kreb‘s cycle:Glucose --6 CO2 + 6H2O +38 ATPs.
  24. 24.  Forms a reservoir of high energy phosphate in the muscle Cannot be used as a direct source of energy. Used for regeneration of ATP from ADP. Creatine phosphatase Creatine phosphate----------creatine + phosphoric acid Phosphoric acid +ADP ------- ATP
  25. 25.  Glucose is stored in the muscle in the form of glycogen. Muscle glycogen is converted into glucose by glycogenolysis. Glucose is oxidized by glycolysis. C6H12O6 + 6O2--------6CO2 +6H2O +38 ATP
  26. 26. Muscle Anaerobic glycogenesis glycogen glycolysis Blood Blood glucose Lactic acidGlycogenolysis Liver Enzymatic glycogen transformation
  27. 27.  The oxidation of lactic acid to carbon dioxide produces energy for the reconversion of ADP to ATP. The lactic acid produced in the muscle contraction passes into blood stream and is transported to the liver. Within the liver, lactic acid is converted to liver glycogen and then to blood glucose. The conversion of lactic acid to glycogen requires oxygen. Muscle glycogen comes only from the glucose of the blood.
  28. 28. ATP acts as a central agent responsible for The actin- The synthesis of myosin The synthesis of phosphocreatineinteraction to glycogen from from creatinecause muscle lactic acid and phosphate. shortening
  29. 29. 1. Conduction of nerve impulse from CNS to neuromuscular junction.2. Depolarization of sarcolemma – influx of Na+ ions & efflux of k+ ions.3. Release of Ca2+ ions from sarcoplasmic reticulum.4. Diffusion of Ca2+ ions to actin filament.
  30. 30.  Binding Ca2+ ions to troponin. Troponin – Ca2+ complex removes tropomyosin blockage of actin sites. Heads of myosin – ATP complex form Cross- bridges to actin filament. Hydrolysis of ATP induces conformational changes in the heads of myosin. 1 mole of Actin + 3 moles of myosin  Actomyosin
  31. 31.  Ca2+ ions sequestered from actin filament by sacroplasmic reticulum. Ca2+ returns to sacroplasmic reticulum. Ca2+ released from troponin – Ca2+ complex. Troponin permits tropomyosin return to blocking position. Myosin-action cross-bridges break. ATP – myosin Complex reformed in heads of thick filament.
  32. 32.  Heat production -liberation of heat is always associated with muscle contraction. Electricity generation -small amount of electrical energy is released. Volume changes –negligible changes in volume occur. Change in optical properties -changes in the birefringence and transparency occur at the muscle fiber. Sound production -muscle sound noted during contraction.
  33. 33.  This theory was evolved independently and more or less simultaneously by A.F Huxley and H.E. Huxley around 1950s. According to this theory, the force of contraction is developed by the cross bridges in the overlap region. The active shortening is caused by the movement of the cross bridges, which causes one filament to slide over the other. During muscle contraction, the actin filaments alone show movement. But the myosin filaments remain static. The mechanical movement utilizes the energy derived from the break down of ATP molecules.
  34. 34.  In the resting state, the cross bridges are in slanting position due to negative charges in both the basal and tips of cross bridges due to the concentration of magnesium ions. After the stimulation of muscle, the release of calcium ions change the electrical character which cause mutual repulsion and shortening of the cross bridges. The attachment of cross bridges on the actin filaments cause sliding of actin filaments while myosin filaments remain static.
  35. 35.  According to this scheme, there are flexible hinges on myosin: one between S1 heads and the long rods and the second between S2 and the LMM at the trypsin reaction site. When the head piece(S1 )binds to the exposed site on actin it is thought to rotate. This type of rotation occurs simultaneously at numerous locations of actin – myosin filaments which cause shortening of the muscle. The energy for this process derived from the hydrolysis of ATP.
  36. 36.  The muscle are biological motors which convert chemical energy into force and mechanical work. This biological machinery is composed of proteins – which is actomyosin and the fuel is ATP. With the use of muscles we are able to act on our environment.
  37. 37.  Dr.B.Victor is a highly experienced professor, recently retired(2008) from the reputed educational institution- St. Xavier’ s College, Palayamkottai, India-627001. He was the dean of sciences, IQAC coordinator and assistant controller of examinations. He has more than 32 years of teaching and research experience He has published 5 research articles in international journals and 32 in reputed Indian journals and guided 12 PhDs. Send your comments to :